The invention relates to a workpiece holder for a machining apparatus, wherein a succession of workpieces is supplied to a least one machining unit and wherein during the machining operation each workpiece is held by the workpiece holder, as well as a machining apparatus having such a workpiece holder.
Different forms, sizes and designs of workpiece holders of the aforedescribed type are known in the art. In particular, workpiece holders are known which have active gripping arms and receive workpieces from a feed unit, hold the workpieces during the machining operation, and subsequently transfer the workpieces to a transport device. Although these workpiece holders have proven successful in practice, they are expensive difficult to maintain due to their moveable active gripping arms. In addition, the conventional workpiece holders come to a stop at the machining unit to allow machining of the workpiece. This limits the throughput of machining apparatuses equipped with corresponding workpiece holders.
In certain applications, the form and structure of the workpiece is not machined, so that the workpiece does not have to be held in a precisely defined position relative to the machining unit. This may be the case where, for example, the workpiece is only cleaned or filled. These applications can be found, for example in the beverage industry, wherein workpieces, such as bottles, are continuously moved past a processing unit, for example a filling machine or a cleaning machine. Here conventional transport units can be used, where in general the position of the workpiece relative to the processing unit does not have to be accurately established. However, if it becomes necessary to fix the position, then the processing unit itself can be provided with grippers which grip the workpiece and hold the workpiece in place for the duration of the operation. Such devices allow a very high throughput, but tend to have rather complex mechanisms. Moreover, such devices cannot be easily employed in or added to conventional machining apparatuses, in particular milling machines, saws or chamfering machines.
It is therefore an object of the invention to provide a workpiece holder that can also be easily employed with and added to simple conventional machining apparatuses, in particular cross-cut machines that include milling and sawing tools, and that provides a high throughput.
The object is solved by a workpiece holder for a machining apparatus of the aforedescribed type, in which at least one continuous clamping chain with a plurality of clamping jaws is provided.
By using a workpiece holder designed in this way, workpieces from a corresponding feed unit can be received continuously using the clamping jaws and guided past a machining unit, such as a saw or milling machine, without a need to stop the machining operation. It should be noted, that a continuous belt, similar to a conveyor belt, can also be used instead of the continuous chain. In the simplest embodiment, it may be sufficient to employ only a single clamping jaw.
The clamping jaw can be an active clamping jaw with moveable clamping elements. However, a passive clamping jaw is preferable due to its simpler design, ease of maintenance and inexpensive manufacture. In this case, the clamping action is effected solely by, for example, guiding of the clamping chain along a slide rail disposed opposite the open side of the clamping jaws.
The clamping chain can be guided and driven in various ways. Preferably, the workpiece holder includes drive and guide means in the form of two cylinders that drive and guide the clamping chain along a predefined pathway. If a slide rail which acts as a counter pressure element is provided along the region of the pathway, where the workpiece to be machined has to be securely clamped, then the workpiece holder needs only have a single clamping chain.
In a preferred embodiment, the workpiece holder includes two clamping chains with complementary clamping jaws. Under normal operating conditions of the workpiece holder, the two clamping chains move in opposite directions and parallel to one another along a section of the respective path, thereby providing a secure support of the workpiece to be machined along this section. A workpiece holder implemented in this way not only provides an especially high throughput, butxe2x80x94in cooperation with suitably formed feed meansxe2x80x94also grips and guides the workpieces so as to prevent the workpieces from being damaged. The clamping chains can revolve continuously, so that the workpiece holder does not have to be constantly braked and then again accelerated, which improves its durability.
According to another preferred embodiment of the invention, pressing means can be provided that press the clamping jaws towards a workpiece along a machining path. The pressing means can have any form that is optimized for the respective application. In particular with cross-cut machines, it has proven advantageous to implement the pressing means in form a pressing rail. The pressing rail can be formed so that the pressure exerted on the clamping jaws is variable. This arrangement allows, for example, workpieces with different diameters and/or different friction coefficients to be securely held by the clamping jaws without damaging the workpiece.
If the pressure exerted by the pressing rail on the clamping jaws is to be variable, then the pressing rail is preferably designed so as to be formed of a plurality of pressing elements, wherein each pressing element can be pre-biased and/or moved towards the clamping jaws using its own mechanical, hydraulic or pneumatic pressing means, in particular springs. The pressing elements can be arranged in an overlapping fashion, so that the resulting pressure that is applied via partitioned rams using the individual pressing means is uniform. The pressing elements can be used to apply a preferably variable pressure to each revolving clamping jaw, thereby optionally forming a feed and discharge region with a low pressing force and a holding region with a high pressing force. The pressing force can also be varied from location to location during the machining operation depending on the specific machining task.
In another preferred embodiment, each clamping jaw has at least two clamping pockets, preferably with different profiles. These pockets can be formed, for example, as recesses with different apex angles, e.g., 90xc2x0 and 120xc2x0, so that such clamping jaw can be used to grip and clamp round profiles as well as hexagonal and rectangular profiles.